Generally speaking, attorneys have implied authority over legal and tactical matters, while the client has the right to make strategic decisions on factors such as expenses or calling witnesses. (lawyerist.com)
Implied authority of an agent is the result of authority implied by reason of the agent's relationship with the principal of the principal's business, by reason of custom and usage, and by acquiescence. (law.stackexchange.com)
So what about finding a relevant implied authority in the AUMF under other principles of statutory interpretation? (opiniojuris.org)